Gas (combustion) turbine engines are used for generating power in a variety of applications including land-based electrical power generating plants. The precise control of combustion dynamics is critical for the proper operation of a gas turbine engine. The fuel and air mixture is ignited and burned in the combustor section of a gas turbine engine under extremely high pressure and temperature conditions. Dynamic pressure waves having a frequency ranging from a few hundred hertz to a few thousand hertz occur during the combustion process. If these pressure pulses become excessive, mechanical damage can result in the turbine combustor and downstream components. Increasing the flame temperature can stabilize the combustion process. This approach, however, will increase the production of undesirable nitrogen oxide emissions. Accordingly, there must be a balance between the concerns of reduced emissions and stable combustion.
It is known to utilize active control of the combustion process in order to achieve stable, efficient, regulation-compliant operation of a gas turbine engine. Active control systems typically include a sensor for detecting a parameter responsive to the combustion process and a control element for controlling the combustion process in response to the measured parameter. One or more such parameters may be measured; for example, the parameter may be the pressure in the combustion chamber, a sound produced by the engine, a predetermined wavelength of electromagnetic energy generated by the combustion process, or the exhaust concentration of a particular combustion byproduct such as carbon monoxide. One such gas turbine active combustion control is described in U.S. Pat. No. 5,428,951, incorporated by reference herein, wherein a pressure sensor is used to detect combustion-induced pressure oscillations. The mounting arrangement for the pressure sensor is not described in that patent. Another U.S. Pat. No. 5,706,643, incorporated by reference herein, illustrates an active gas turbine control system wherein a pressure probe is mounted to a combustor wall, with a pressure signal being routed to the outside of the engine case by an electrical wire connection. The pressure probe and wire connection are thus exposed to the harsh environment inside the engine casing.
Gas turbines are known to include a compressor producing compressed air, a combustor combusting a fuel in the compressed air to produce a combustion gas, and a turbine receiving the combustion gas and expanding the combustion gas to extract mechanical energy. FIG. 1 illustrates a gas turbine engine 10 provided by Siemens Westinghouse Power Corporation, the assignee of the present invention. The engine 10 includes a combustion chamber 12 defined by a combustor wall 14. A burner assembly 16 provides a mixture of fuel and air for combustion in the combustion chamber 12 where the combustion gas is produced. These components are housed within a casing 18 that forms the atmospheric pressure boundary of the machine. A pressure transducer 20 is mounted outside the casing 18 for measuring pressure fluctuations within the combustion chamber 12 for use with an active combustion control system. The transducer 20 is installed into a mounting block 22 having a fluid connection to the combustion chamber 12. The fluid connection is established through a hole 24 formed through the “top hat” of the casing 18 to which is connected a communication tube 26. The communication tube 26 extends along the longitudinal length of the burner assembly 16 and is connected, such as by welding, to a port 28 formed on the combustor wall 14. The port 28 is installed in the same axial plane as an end of a pilot cone 30 of the burner assembly 16. A fitting 32 is welded to the casing 18 and the mounting block 22 is connected to the fitting 32. A damping tube 34 is connected to the opposed side of the mounting block 22 via union 36 in order to eliminate the acoustic resonance inherent in the length of the communication tube 28. This arrangement has the advantage of keeping the transducer 20 outside of the casing 18, which simplifies replacement of the transducer and avoids exposure of the transducer 20 to the environment inside the engine 10. However, this system permits the pressure internal to the engine 10 to extend beyond the casing 18, and therefore, the pressure boundary created by the mounting block 20, fitting 32, union 36 and damping tube 34 must be properly protected against mechanical damage. Furthermore, the volume enclosed by the communication tube 26 and damping tube 34 may affect the pressure oscillations experienced by the transducer 20.
Accordingly, an improved apparatus for sensing pressure oscillations in the harsh environment of a gas turbine engine is desired.